The present invention relates generally to organic photoconductive materials and electrostatic imaging processes, and particularly to improvements in photoconductive polyimide films through formation of polyimide-electron donor charge transfer complexes.
Materials which behave as insulators in darkness but conduct electricity when illuminated or irradiated are known as photoconductive materials, or more commonly, as photoconductors. Such materials provide the basis for electrostatic imaging processes, which are used in certain manufacturing processes, particularly in the electronics industry, and in document copying.
Use of polyimides as photoconductive elements is disclosed in U.S. Pat. No. 3,554,744. However, formation of polyimide-electron donor charge transfer complexes to enhance photoresponse is not disclosed. U.S. Pat. No. 4,368,319 discloses selected polyimide species incorporating aliphatic groups comprising "electron donors", which are defined to be heteroatoms such as oxygen or sulfur, or nitrogen-containing radicals. Treatment of polyimides to form polyimideelectron donor charge transfer complexes is not disclosed.
Gordina, et al., Visokomolekulvarnie soedineniya (B)15:378 (1973) disclose that aromatic polyimides are intrinsic donor-acceptor materials and that they form charge transfer complexes with added electron acceptors.
British Pat. No. 1,150,435 discloses addition of certain electron donors to a number of so-called "organic binders". Polyimides are included in the list of binders. The patent does not disclose the electron donors employed in the instant invention, nor does it appear that patentees formed or could have formed charge transfer complexes. The electron donors are described as photoconductors and patentees add them to a binder to impart donor photoconductivity to the binder.
U.S. Pat. No. 4,363,860 discloses addition of the acid acceptor, trinitrofluorenone, to polyamic acid followed by imidization.